Transistors such as metal oxide semiconductor field effect transistors (MOSFETs) or simply field effect transistors (FETs) or MOS transistors are the core building blocks of the vast majority of semiconductor integrated circuits (ICs). A FET includes source and drain regions between which a current can flow through a channel under the influence of a bias applied to a gate electrode that overlies the channel. Some semiconductor ICs, such as high performance microprocessors, can include millions of FETs. For such ICs, decreasing transistor size and thus increasing transistor density has traditionally been a high priority in the semiconductor manufacturing industry. Transistor performance, however, must be maintained even as the transistor size decreases.
A FINFET is a type of transistor that lends itself to the dual goals of reducing transistor size while maintaining transistor performance. The FINFET is a three dimensional transistor formed in a thin fin that extends upwardly from a semiconductor substrate. Transistor performance, often measured by its transconductance, is proportional to the width of the transistor channel. In a FINFET, the transistor channel is formed at least along the vertical sidewalls of the fin, so a wide channel, and hence high performance, can be achieved without substantially increasing the area of the substrate surface required by the transistor.
FINFETs have historically been formed using silicon-on-isolator (SOI) substrates. A SOI substrate includes a silicon material layer overlying an insulator layer, such as a silicon oxide layer. Using the SOI substrate, the conductive fins are formed from the silicon material layer while the insulator layer provides clear demarcation of the base of the fins to electrically isolate the FINFETs. Electrical isolation, e.g., between source and drain regions of FINFETs and/or between adjacent FINFETs, is important for reducing or minimizing electrical current leakage which is a parasitic effect that degrades performance of the integrated circuit.
Bulk semiconductor substrates, such as bulk silicon substrates, are less expensive than SOI substrates, and FINFETs can also be fabricated using bulk semiconductor substrates. A bulk semiconductor substrate is, for example, a monolithic block of single crystal silicon. When a bulk semiconductor substrate is used to fabricate FINFETs, there is no inherent isolation layer and thus no clear demarcation of the base of the fins to electrically isolate the FINFETs. Therefore, an isolation methodology is needed to reduce or minimize electrical current leakage, e.g., between source and drain regions of FINFETs and/or between adjacent FINFETs. Unfortunately, conventional isolation methodologies for FINFETs that are formed using bulk semiconductor substrates are complex, inherently difficult to control, and/or require uniform thickness of the fins.
Accordingly, it is desirable to provide methods for fabricating an integrated circuit with FINFETs using a bulk semiconductor substrate in which the FINFETs are electrically isolated to reduce or minimize current leakage. Moreover, it is desirable to provide methods for fabricating an integrated circuit with FINFETs using a bulk semiconductor substrate and which include improved isolation methodologies for the FINFETs. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.